Shaggy, Shovel-Headed Rhino Evolved in Tibet

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Woolly rhinos and many other large, shaggy prehistoric animals
first evolved their cold tolerance in Tibet, which served as the
evolutionary cradle for Ice Age mega plant-eaters, according to a
new paper.

The study helps explain why so many different species roamed
North America, Europe and Asia during the last Ice Age beginning
about 2.8 million years ago. They had previously adapted to cold
environments in the western Himalayas before later expanding to
other regions.

Several were big with long hair.

"There is a general principle, called Bergmann's Rule, that
suggests animals tend to increase their body size in colder
environments," said Xiaoming Wang, co-author of the study which
appeared in this week's Science. "Large-bodied animals
have relatively smaller surface areas to lose heat and thus
conserve heat better -- it's a matter of physics."

Wang and his colleagues identified Tibet as the mega herbivore
cradle after discovering a new woolly rhino, Coelodonta
thibetana, dating to 3.7 million years ago. As its name
suggests, this animal was about as furry as a beast can be, and
it had a head that functioned like a snow shovel.

"The extinct Tibetan woolly rhino had developed special
adaptations for sweeping snow using its flattened,
forward-leaning horn to reveal vegetation, a useful behavior for
survival in the harsh Tibetan climate," Wang explained.

He and his team suspect that the rhino evolved from
Stephanorhinus, a genus of Eurasian-wide distribution.
C. thibetana then lived during the Pliocene (5.3 to 2.6
million years ago) at a time, Wang said, "when global climate was
much warmer and the northern continents were free of the massive
ice sheets seen in the Ice Age later. The Tibetan rhino likely
was thus able to accustom itself to cold conditions in high
elevations and become pre-adapted for the future Ice Age
climate."

Tibet also gave rise to other cold-adapted animals. While woolly
mammoths and woolly rhinos bit the proverbial dust some time ago,
other species with Tibetan ancestry survived to modern times.

The Tibetan wild yak, for example, is a sister species to
European and North American bison. During the Pleistocene, the
Tibetan wild ass expanded its population to northern Pakistan and
possibly even to Alaska. Snow leopards and blue sheep are two
other examples.

"Like the woolly rhino, blue sheep descended down from high Tibet
during the Ice Age, presumably for the same reason as the rhinos,
but somehow the blue sheep survived to the present day in the
high plateau," Wang said.

The Tibetan antelope is now confined to the highest elevations of
Tibet and adapted "by evolving one of the finest under furs,"
often used by local people to weave highly prized shawls.

The Tibetan antelope and virtually all other modern, cold-hardy
species are now under threat due to climate change and
over-hunting. According to Wang, "The polar bear is a poster
child example" of such animals that are presently at risk.

Animal experts largely agree that Tibet was indeed the birthplace
for many species that later survived through the Ice Age and
beyond.

"We know from today's species that they move up and down
mountains in accordance with climate change," said Adrian Lister,
a professor in the Department of Paleontology at The Natural
History Museum in London. Lister added that "many are now moving
upwards" in an attempt "to escape global warming. It seems
perfectly reasonable that a similar thing could have happened
over longer time scales in the past."

Anthony Barnosky, a professor in the Department of Integrative
Biology at UC Berkeley and a curator at the university's Museum
of Paleontology, said the study demonstrates "the importance of
isolated areas as cradles of evolution."

Wang and his team are already planning future studies in Tibet,
where they "have barely scratched the surface."

"Cold places such as Tibet, the Arctic and Antarctic are where
the most unexpected discoveries will be made in the future," Wang
predicts. "These are the remaining frontiers that are still
largely unexplored."